The present disclosure relates to aperture stops in general and in particular, to a variable, apodizable aperture stop with no moving parts.
Optical devices such as cameras, video recorders, telescopes and satellites include an aperture stop that controls the amount of light passing through the lens of the device. The size of the aperture is typically controlled by mechanical means. For example, in the case of a camera, the lens' diaphragm may be made from thin metal blades that overlap. A rotatable aperture control ring is fitted around the barrel of the lens, and the blades move smoothly toward or away from the center of the lens upon rotation of the control ring, which in turn results in the aperture being reduced or enlarged in radius. Alternatively, a movable sheet having a plurality of apertures of different sizes may be placed in front of the lens to achieve the desired aperture size. With such a configuration, however, the number and range of aperture sizes available is necessarily limited.
As with all mechanical devices, such mechanical aperture stops are subject to wear and tear and thus have a limited life. For the same reasons, they often are prone to becoming unreliable, which is especially problematic in space applications where faulty aperture stops cannot be easily or quickly serviced. In the case where repair or replacement of the aperture stop is not possible, the optical device is rendered useless. Mechanical aperture stops are also vulnerable to environmental disturbances such as high shock or vibration and temperature variations, which is especially problematic in harsh environments like space. In addition, due to the mechanical nature of such aperture stops, movement of the optical device in which they are placed is often inevitable, which has an adverse affect on the quality of the images produced. This is especially problematic in applications in which movement of the optical device cannot be tolerated such as in space, where focus may not be adjustable.
Another significant problem associated with mechanical aperture stops is the occurrence of diffraction at the sharp edges of the aperture. When observing space scenes, the excessive glare resulting from such diffraction is especially problematic. The size of mechanical aperture stops also makes them unsuitable for applications requiring a high degree of miniaturization. In today's technological world where smaller is better, such aperture stops are highly undesirable.
Accordingly, there is a need for a variable, apodizable aperture stop having no moving parts.